The Nautical Almanac and The Sight Reduction Tables for Marine Navigation (Publication 229) reduce calculations and spherical trigonometry to tables. Your observed measurements with the sextant, combined with data from these tables allow you to obtain the necessary coordinates to plot a Line of Position with some simple addition and subtraction. This process, called a sight reduction, is guided by the Sight Reduction Form. In this manner, multiple Lines of Position may be plotted to obtain your position.

If you have not already printed out a copy of the Sight Reduction Form to assist with the lesson, please do so now.

This section covers how to use the publications, your observations with the sextant, and the time to obtain a Line of Position using the four parts of the Sight Reduction Form:
Section I: Observations and Corrections
Section II: Time and Dead Reckoning
Section III: Latitude and Longitude
Section IV: Determining a Line of Position

To start this section, click the video for Section I above.